Effects of 1,2-dibromo-3-chloropropane on hepatic heme synthesis

Liver delta-aminolevulinate dehydratase activity in amitriptyline- or chlorpromazine-treated rats

Amitriptyline (AMT) and chlorpromazine (CPZ) (0.5 mg per animal, i.p.) were injected into rats separately for 30 days and their effects on heme metabolism in liver were examined. Significant decreases in the delta-aminolevulinate dehydratase activity were observed following the administration of both drugs (mean value of AMT-group: 6.58 U/g tissue; and CPZ-group: 7.04 U/g tissue) in comparison to that of controls (11.71 U/g tissue); however total liver heme content was not altered. When 24-h urinary excretions of delta-aminolevulinate (ALA) and porphobilinogen (PBG) were measured on the last day of the experiment, a slight (AMT-group: 38.40 micrograms/day) to distinct (CPZ-group: 59.11 micrograms/day) increase of urinary ALA was observed, while PBG excretion tended to decline only moderately under CPZ (3.52 micrograms/day), but significantly in presence of AMT (2.16 micrograms/day). Mean values obtained from control group were 32.12 micrograms/day for ALA and 4.25 micrograms/day for PBG.

Sodium cholate extraction of rat liver nuclear xenobiotic-metabolizing enzymes

DNA is the purported target of several carcinogenic and mutagenic agents. Nuclear enzymes which could generate or detoxify reactive metabolites are of major concern. Several such enzymes have been identified within nuclei, but obtaining samples with enriched content or activity is difficult, time-consuming, and uses harsh isolation techniques. Extraction of rat liver nuclear suspensions with cholate-containing buffer results in solubilization of 25-30% of the protein. Linear extraction was obtained for total protein and cytochromes P-450 and b5, NADPH-cytochrome P-450 reductase, NADH-cytochrome b5 reductase, DT-diaphorase, and microsomal-like epoxide hydrolase with specific activities comparable to values reported for isolated nuclear membrane, while the yield was five to ten times greater. Detergent extracts of rat liver nuclei were employed to study the comparative response of microsomal and nuclear enzymes to chemical treatment. While the responses to acute inductive (phenobarbital and 3-methylcholanthrene) and toxic (carbon tetrachloride and dibromochloropropane) treatments were qualitatively similar, an initiation-promotion protocol (diethylnitrosamine with phenobarbital promotion) resulted in divergent responses between the enzymes in the two subcellular fractions. Detergent extracts of nuclei offer an efficient means of recovering xenobiotic-metabolizing enzymes from rat liver nuclei, and have been utilized to demonstrate a differential response of nuclear enzymes during preneoplastic development.

Immunofluorescent determination of the lobular distribution of a constitutive form of hepatic microsomal cytochrome P-450

We have used an immunohistochemical approach to study the lobular distribution of constitutive liver microsomal cytochrome P-450. Cytochrome P-450 isolated (10.3 nmoles per mg protein) from hepatic microsomes from untreated, mature male Sprague-Dawley rats was used to produce antisera in rabbits. The IgG fraction produced single precipitin lines of identity with liver microsomes after double immunodiffusion, precipitated 80% of the total microsomal cytochrome P-450 and inhibited three cytochrome P-450-dependent enzyme activities. By these criteria, the IgG appeared to be specific for a constitutive form (or immunochemically related family) of liver microsomal cytochrome P-450. The pattern of fluorescence after indirect immunofluorescent labeling of liver sections depended on the route of tissue preparation and the concentration of primary antibody. In frozen sections, the labeling was uniform throughout the lobule, whereas in "antigen-depleted" paraffin-embedded sections it was heaviest in the centrilobular and midzonal regions. Increasing the concentration of primary antibody to 500 micrograms per ml inhibited the centrilobular labeling in frozen sections in a concentration-dependent manner. When specific isozymes of cytochrome P-450 were induced with phenobarbital or 3-methylcholanthrene, the constitutive cytochrome P-450 was localized predominantly in the periportal region. Decreases in cytochrome P-450 in rats treated with carbon tetrachloride or 1,2-dibromo-3-chloropropane were associated with antigen loss only in necrotic cells. Regional differences in the loss of antigen in paraffin sections and the inhibition of fluorescence in frozen sections establish that the lobular distribution of constitutive hepatic microsomal cytochrome P-450 is qualitatively heterogeneous and may be altered during hepatocellular responses to chemical treatment.